Ask The Expert

October 21, 2013

Peanuts and Anaphylaxis Due to Cashew Nut

Question:

Recently I saw a one year-old child with a history of well-controlled eczema with anaphylaxis to cashew nut. His SPT was 13 mm wheal to pistachio (cashew was unavailable) and his specific IgE was 7.44 to both cashew and pistachio. He has never been introduced to peanut. His SPT to peanut was 4 mm (PC Histamine was 9 mm). His specific IgE is unavailable but ordered. His mother is wondering if it is safe to feed peanut butter with his history especially without prior exposure. My current recommendation was to definitely avoid all tree nuts (here is another twist – he can tolerate almond milk) and peanuts due to the potential of developing reactivity to peanuts; however, I also read that he most likely will be able tolerate peanuts.

From the Editors: The clinical management of patients with one or two known tree nut allergies who have never ingested peanuts or another tree nut is a problem faced by most allergists on a weekly basis. Read what our experts recommend.

By Prof. Katrina Allen

Despite the lack of cashew SPT result, the child’s high specific IgE to both cashew and pistachio in the context of an objective acute allergic reaction to cashew strongly supports the diagnosis of confirmed cashew allergy and probably pistachio allergy. Cashew and pistachio allergies commonly co-associate clinically.

There are some allergists who do not undertake screening to other nuts that have not been ingested because of the high false positive rate. However, in the context of a patient with a history of confirmed cashew anaphylaxis it in not unreasonable to undertake screening for peanut and other tree nuts since approximately 25% of those with an allergy to peanut are also allergic to tree nuts (Marco Ho et al JACI 2008).

In this context it might be worth considering doing an Arah2 serum test (component resolved diagnostics) since the test has high specificity and sensitivity for peanut allergy (Thanh Dang et al JACI 2013). Read the entire answer

By Dr. Wesley Burks

Although there are not a lot of studies to give us the right answer in this situation, the best way forward would be to do a peanut challenge, and then if the child tolerates the challenge, to incorporate peanuts into their diet.